1. Field of the Invention
This invention generally relates to semiconductor processing, and, more particularly, to the formation of transistors.
2. Description of the Related Art
In general, there has always been, and continues to be, a desire to make semiconductor devices smaller. Reductions in the size of semiconductor devices provides numerous benefits. For example, all other things being equal, the production yields of semiconductor devices with a smaller feature size are increased because more devices may be fabricated on a single wafer. Additionally, smaller feature sizes may also result in increased electrical performance of the completed integrated circuit device.
In traditional field effect transistors, the gate electrode may be made from a doped polysilicon. The particular dopant material selected and the concentration of the dopant material will depend, in part, on the technology involved, e.g., NMOS, PMOS or CMOS, as well as the desired electrical performance characteristics of the semiconductor device under consideration.
One of the problems associated with using doped polysilicon as the gate electrode is the lack of uniform distribution of the dopant material throughout the polysilicon after the dopant material is initially applied. The non-uniform distribution of dopant material is particularly problematic at the interface of the gate electrode and the gate oxide.
Attempts to alleviate this problem have typically included subjecting the doped polysilicon gate electrode to one or more heat treatments. The purpose of these heat treatments is to more evenly distribute the dopant material in the polysilicon and to drive more of the dopant material deeper into the polysilicon, i.e., toward the interface of the polysilicon gate electrode and the gate oxide.
However, the use of heat treatments to attempt to rectify the above problems causes other problems in the fabrication of semiconductor devices. For example, when a semiconductor device is heated to more evenly distribute the dopant material in the polysilicon, other doped regions in the semiconductor device may also experience a spreading of the dopant material from its original site. To account for this undesirable spreading of doped regions during heat treatments, semiconductor devices are designed such that the affected doped regions are spaced farther apart than they would be if no such heat treatments were applied to the semiconductor device.
The present invention is directed to a method and device that solves some or all of the aforementioned problems.